1. Field of the Invention
The invention relates to a moving body posture angle detecting apparatus, and more particularly, to technology that accurately detects a posture angle of a moving body such as a robot.
2. Description of the Related Art
Acceleration sensors and angular velocity sensors are used in posture control of moving bodies such as robots. When three orthogonal axes are designated as an x axis, a y axis, and a z axis, the accelerations in the directions of these three axes are detected by three acceleration sensors and the angular velocities in the directions of the three axes are detected by three angular velocity sensors. The angles around the axes, i.e., posture angles, are obtained by time-integrating the outputs from the angular velocity sensors such that the pitch angle, the roll angle, and the yaw angle can be calculated. Japanese Patent Application Publication No. JP-A-2004-268730 describes technology which performs posture control using posture data and acceleration data output from gyro sensors.
When the offset and drift of the angular velocity sensors (yaw rate sensors) are large, however, the offset and drift values accumulate gradually and end up being extremely large values because the posture angle is obtained by the integration of the angular velocity. Those values increase with time and ultimately diverge. This problem can be avoided by using angular velocity sensors with little offset and drift, but these kinds of sensors are large, heavy, and expensive.
On the other hand, it is possible to correct the accumulation of errors from integration by detecting the gravitational direction with an acceleration sensor and correcting the posture angle obtained by the angular velocity sensor at an appropriate timing using this gravitational direction. Unfortunately, however, this method is unable to be used when the changes in movement of the moving body are fast and acceleration other than gravity is frequently generated.